Composition for use in making sulphate or kraft pulp and process of making same



Patented May 17, 1927.

UNITED STA Es PATENT OFFICE.

HERMAN B. SKIPPER, or MUSKEGON, MICHIGAN".

' COMPOSITION ronnsn 11v MAKING SULPHATE'OR KRAFT rULr nnnrnocnss or MAKINGSAME.

No Drawing.

This inventionrelatesto materials for use in the manufacture of paper, and more particularly sulphate orkratt pulp, and to processes of producing such materials.

In themanutacture of sulphate or krai't pulp, a' solution containing principally'sodium hydroxide and sodium sulphide is used to digest the Wood to pulp. Sodium sulphate, or salt cake is the chemical marketed for these operations and this is reduced by the pulp manufacturer to sodium sulphide. The sodium sulphide largely loses its sulphur during the digestion process with the formation of sodium carbonate which is black liquor, the latter being evaporated, and the sodium carbonate thus obtained being converted into sodium hydroxide by means of lime. -Attempts have been made to use nitre cake or sodium acid or hydrogen sulphate for reductionto sodium sulphide. But because of the tree sulphuric acid in this compound its use has been restricted, since this free acid corrodes certain parts of the furnace and evaporation apparatus.

One or the objects of the present inven- 1 'tion is to make it possible to use nitre cake without danger of corrosion of the "apparatus.

Other and further advantages and objects of this invention will appear from the more detailed description set forth below, it being understood that .various changes may be made herein by those skilled in the art, without departing from the scope and spirit of this invention.

Fundamentally,-' this invention comprises the neutralization of the free acid in the niter cake so that the latter is rendered available for use in the sulphate or kraft process. This neutralization may be effected in a number of different ways. In one case, sodium carbonate may be added to the niter cake in such proportion as to neutralize the free sulphuric acid present, and the two substances thoroughly are ground and mixed together so that they may be fed to the res duction furnaces Without fear of injury to the latter orto the evaporation apparatus.

Instead of sodium carbonate, there may be used what is known as fishedlsalts which is a by-product secured from commercial processes of making caustic soda.

Application filed November 26, 1924. Serial No. 752,465.

These fished salts may be added to the ground nitre cake and themixture' may be heated duringthe mixing eration. .There' is thus obtained a pracand grinding optically neutral salt cake,'or sodium-sulphate v for use in the reduction furnaces.

I urthermore,the'nitre cake may bemixed with either the sodium carbonate in desired proportion, or With the fished salts as the case may be, and the mixture may-be dissolved directly in the black liquor before the latter enters the disc or other evaporators.

I WVhile there has been set forthabove the returned irom the digestion as spent or take, it is obvious that the free acid in the nitre cake may be neutralized by a mixture of sodium carbonate with fished salts in i any desired proportion of these ingredients, the proportion of the mixture. in the preferred case being that required to form With the acid sulphate, sodium sulphate.

I The processes, set forthabove afford a i very desirable and inexpensive method of using 'nitre cake in making sulphate or kraft pulp. 7

As will be understood by those skilled in the art, the term spent or black liquor from the kraft process is meant the aqueous solution of various soluble salts such as sodium carbonate, and the insoluble ingredients mixed with said solution and secured from the digestion of the pulp.

The organic matter contained in such black liquor is burned .in the recovery process and the sodium salts, more especially the sodium carbonate, are causticized to yield sodium hydrate and are neutralized in the pulp digestion.

' It will also be understood by those skilled in the art that by the term fished salts is meant the Waste or by-products obtained from the manufacture of caustic soda. These salts consist principally of sodium hydrate-sodium carbonate, and sodium sul phate.

Having thus set forth my invention, I

claim V 1 1; A composition for making kraft pulp comprising sodium hydrogen sulphate and 2. A composition'for use in kraft 1 pulp manufacture comprising sodium hydrogen' pulp comprising nitre calze, sodium car houate, 'an'd lisli ed' salts.

5. A process of making a composition for use in kraft pulp mauu pcture p'hicl'iconiprises mixing sodium hydrogen sulphate and ilished salts: and reducing themixture.

(5. A process of nudging a composition for use in kraft pulp manufacture which compr ses mixing and grinding together sodiiun'hydrogen sulphate and. sodium car-v honate in such proportions as to yield sodium sulphate and reducing the mixture.

7. processo'l making a composition for use in sulphate pulp manufacture which comprises mixing sodium hydrogen sulphate and sodium carbonate With black liquor and evaporating the mixture. i

8. A process pf making a cgmpgsition for use in lifa'l't pulp manufacture which comprises mixing sodium hydrogen sulphate and fished salts -v in such proportionsas to yield sodium sulphate, with black liquor andevaporatingthemixture. v i

In testimony whereof I have hereunto set my handv i HERMAN Blimp-PER. 

